Breast cancer is an uncontrolled growth of cells in breast tissue caused by a genetic abnormality, resulting in malignant tumors, typically originating from the inner lining of milk ducts, glands that supply the ducts with milk, or less commonly, from the fatty and fibrous tissues.1 Nearly all cases of breast cancer occur in women.2 Statistically, breast cancer accounts for the most deaths caused by all other cancers except lung cancer, and about one in eight women who reach the age of eighty will have developed breast cancer.1 Older women are more at risk of having breast cancer.
In early stages (i.e., stage 0 and stage 1A) of breast cancer, cancer cells stay in the breast. As the cancer progresses, cancer cells eventually spread into the underarm lymph nodes. Lymph nodes are small organs of the immune system located throughout the body, including the armpit, which are linked by vessels. If cancer cells spread into the lymph nodes, they have access to other parts of the body.
Early detection is paramount to preventing breast cancer from progressing to dangerous stages. If detected in its early stages, it is likely that the tumor is small and still confined to the breast and therefore more likely to be treated successfully. However, if the tumor is not detected until it has grown large and spread into the lymphatic system, chances of survival are greatly decreased. Therefore, it is important that women be screened often to catch the cancer early and increase their chances of survival. Unfortunately, there is no device available that a woman may use to regularly screen herself for breast cancer at home. Currently, alternative detection and screening methods exist, including physical examination, genetic screening, mammography, ultrasound-based screening, and breast magnetic resonance imaging (MRI), among others. A clinical or self-performed breast examination involves feeling the breast for abnormalities. It is not an effective preventive method because finding a lump likely indicates that the tumor has already been growing for years. There is no evidence that routine examination reduces morality rates, and it is no longer a recommended screening method.
Genetics play a minor role in determining risk factors. Genetic testing focused on inherited BRCA1 and BRCA2 gene mutations allow women to assess a risk profile for developing breast cancer before a certain age. Such genetic screening does not detect the presence of breast cancer, but it may reveal a person's susceptibility to develop it. The U.S. Preventive Services Task Force, composed of primary care and prevention experts, recommends against routine testing unless family history suggests a higher risk of BRCA1 or BRCA2 mutations. Having a close relative diagnosed with breast cancer increases a woman's risk of breast cancer. However, about eighty-five to ninety percent of breast cancers occur naturally in women who have no family history of breast cancer. Only five to ten percent of occurrences are caused by inherited mutations. Therefore, to detect breast cancer early, it is important to perform regular testing rather than rely on one's susceptibility to breast cancer. Moreover, since only a small percentage of breast cancer occurrences is caused by inheriting mutations, it is not a method that would be beneficial for the general public.
The two leading techniques for breast cancer screening are mammography (see FIG. 1A) and magnetic resonance imaging (MRI). Mammography is a diagnostic and screening procedure whereby low-energy X-rays are used to create images, which are then reviewed by a physician for signs of cancer. The American Cancer Society recommends that women over the age of forty receive a screening mammogram every year. Some studies show that the decrease in rate of breast cancer deaths is due to mammography. However, there is continued debate about whether this method is less helpful than it is helpful. For example, one of the drawbacks is that false positives create long-lasting psychological stress and anxiety, which can affect the patient's wellness and behavior for many years. On the other hand, false negatives estimated up to thirty percent occur, which can lead to missed opportunities for treatment if regular checking is not done. Mammograms do not work well in younger women because their breast tissue is denser. Cost can further be an issue, more so because insurance policies tend not to cover mammograms for women under forty, even though women in their teens or twenties are sometimes diagnosed with breast cancer. Ultimately, it has been shown that death rates over 25 years were the same among women ages 40 to 59 regardless of whether or not they underwent regular mammograms. Other drawbacks include discomfort and limitation in detection accuracy. Patients undergoing mammograms have their breasts compressed, which can cause pain or discomfort. Tumors sized smaller than one millimeter are difficult, if not impossible, to detect. Given the balance of benefits, drawbacks and costs, overtreatment by mammography is common. Medical ultrasonography is a supplement to mammography that uses ultrasound to image breast tissue that is denser or deeper in from the surface of the skin. While it increases the detection rate of breast cancer, it also increases the rate of false positives. Ultimately, even purely ultrasound-based screening may warrant an invasive biopsy procedure to confirm whether a tumor exists in the tissue sample removed from the patient's body and determine whether that tumor is benign (non-cancerous) or active (malignant).
Breast MRI is an alternative to mammography. Breast MRI may also be recommended to accompany mammography in women at high risk for breast cancer. In MRI, magnets and radio waves are used to create pictures of the breast and surrounding tissue. Its main benefit over mammography is that it dramatically reduces false negatives, giving a negative result great certainty in ruling out the presence of cancer. Breast MRI is more sensitive and able to detect the presence of cancer cells that are not detectable via mammograms, including tumors that are too small, tumors within dense tissue material, and tumors that are clearly benign. However, it also produces greater false positives and is expensive, costing thousands of dollars. It requires a specialist to administer the MRI and interpret the results. It is a time-consuming and invasive procedure requiring injection of a contrast agent that poses a risk to patients with a history of renal disease. Patients with metallic substances inside them, such as a pacemaker or breast reconstruction material, also may not use MRI. Thus, MRI is reserved for certain types of patients, such as those with family history of breast cancer, those who are at genetic risk, or those who have dense or abnormal breast tissue (e.g., implants, scars, augmentations).
Both mammography and breast MRI procedures require a biopsy (see FIG. 1B) to histopathologically verify the presence of cancerous tissue, because not all breast tumors are cancerous and in need of removal. During a biopsy, a physician takes a sample of tissue from the suspicious area of the breast and tests it for cancer. Up to seventy-five percent of biopsies performed on tissue determined to be cancerous by mammogram and MRI have been found to be benign. Removing tissue from the breast can be a physically and psychologically challenging procedure. There exists a need for a screening technique that eliminates the cost and stress of unneeded biopsies.
Recently, there have been attempts to screen for breast cancer without the need for a biopsy. One such method is the use of computer-aided tomography (CAT scans) for breast cancer imaging. A dye is introduced intravenously and two-dimensional cross sectional images of the breast are produced. A computer may then combine these images to produce detailed pictures. Currently, this technique is not used for breast cancer screening and is typically only used for large-scale imaging of the entire body to determine if the cancer has spread from the breast area. In addition, this technique is not non-invasive because it requires the injection of the dye as well as a visit to the physician. Similar to the use of CAT scans is the use of fluorescent probes and near-infrared radiation (NIR). To use fluorescent probes, a drug is introduced to the test subject intravenously that will preferentially absorb into cancerous cells. It then interacts with the cells in vivo to produce a dye whose fluorescence may be imaged when exposed to a particular wavelength of light. While the use of light in the NIR range has the advantage of being highly sensitive and specific (can also reach deep tissue), it has the same problems as CAT scans in that it requires the injection of a drug and cannot be performed without the aid of a physician.
NIR can be used in a less-invasive technique that studies oxygen metabolism and blood volume in tissue. Since tumors grow more rapidly and require more nutrients than normal tissue, tumors also require additional blood vessels to supply these nutrients. Detecting the presence of additional blood volume and changes in blood oxygenation can thus be indicative of a tumor. Through NIR imaging, areas of large hemoglobin density (i.e., cancerous tissue) may be evidenced by areas of shadow when illuminated by NIR light at certain wavelengths because hemoglobin absorbs light at these wavelengths. This technology has the advantage of being non-invasive and capable of use as a home diagnostic device. However, this technology is limited by the difficulty in distinguishing between absorption and scattering in tissue, as well as the need to rely on secondary factors (oxygen metabolism and blood volume) to determine the presence of a tumor.
Breast cancer screening remains an important procedure for women because of breast cancer's implications to their psyche, their body and their very life. Breast cancer has been known for thousands of years, and modern medical successes have allayed confusion from times past and provided ways to potentially save women's lives. Nevertheless, it can be seen that current methods of breast cancer screening and diagnostic methods can be stress inducing, unreliable, bulky, invasive, and costly. Moreover, some women may also feel a stigma associated with breast cancer, and going through medical procedures related to breast cancer can make them feel especially vulnerable to privacy issues.
Therefore, it would be useful and desirable to have a portable, non-invasive device that is handheld and with which women may use to screen themselves for breast cancer without the need to visit a physician. The present invention provides such a non-invasive device that is not only capable of producing high-resolution, three-dimensional images of abnormalities of breast tissue but it can also detect the type of abnormalities and their location using multispectral imaging techniques. As the present invention uses broadband sources and/or multiple coherent sources, secondary factors such as oxygen metabolism or blood volume associated with the cancer tissues could also be detected to provide further verification of the type. Quick delivery of images and results in the privacy of one's home allows the user to interpret the results and decide whether to invest further time and energy by visiting a physician.